1. Field of the Invention
The present invention relates to a water hammer arrester, more particularly, to a water hammer arrester having nitrogen gas, as a medium of reaction force, filled up in an internal pressure chamber formed within a housing and being capable of reducing a whole length of a housing.
2. Discussion of Related Art
In general, a phenomenon such as a water-hammer happens at such a place as a bent part of a pipe line through which a fluid passes, that is to say, where a flow of a fluid is cut off. This water-hammer may cause a big noise as well as a big vibration which can damage the pipe line and further is well known to be a primary factor of the reduction of a building life span.
A water hammer arrester is mounted on a pipe arrangement line against the water hammer which damages a pipe line or a building. The water hammer arrester includes a piston moving to correspond to a change of a water pressure running along the pipe line, a housing having the piston built-in to stand against a water hammer and a nipple for connecting the housing with the pipe line. Consequently, the housing has a predetermined length so that the piston could be operated therein.
The water hammer arrester having this housing is illustrated in Joserb P. Isrnet et al. U.S. Pat. No. 4,819,698 and in Charles H. Perrott et al. U.S. Pat. No. 5,385,172. The housing therein is provided with an internal pressure chamber, in which the piston operates.
The internal chamber is called an air chamber and filled up with air. When the piston goes up by the water hammer, an air pressure is acted by the piston in the internal pressure chamber. If a water hammer phenomenon happens in a pipe line provided with a water hammer arrester, water or gas like a steam running along the pipe line comes rapidly into the housing through a connector and then the piston is pushed within the housing by a fluid.
At this time, the piston compresses an air within the internal pressure chamber and a compressive force of an air becomes bigger the more the piston goes up to an upper direction of the internal pressure chamber by the water hammer. Consequently, as an air pressure working against the piston and a fluid pressure originated by the water hammer are canceled by each other, the water hammer can be prevented.
The internal pressure chamber having a low pressure can stand against a fluid pressure, so that the water hammer could not be prevented. For this reason, the volume of the internal pressure chamber needs to have a predetermined size to make the internal pressure chamber have a predetermined pressure and so the housing is composed to have a predetermined length. The housing has commonly an elongated shape in order for the piston to move therein.
However, as the water hammer arrester is mounted on a pipe arrangement path of a pipe line, on which various pipe lines are arranged, a space for mounting them is very small. As the housing, through which a fluid flows, is mounted on the small space, the smaller a length of the housing is, the better it is.
In the meantime, a size of the internal pressure chamber of the housing in a conventional water hammer arrester is calculated by summing up a volume occupied by the piston and a volume filled up with a reaction force medium in the upper piston. The length of the housing is determined according to the above described volume. In other words, as for the calculated length of the housing, the length corresponding to the volume occupied by the piston is distinctly distinguished from the length corresponding to the volume filled up with the reaction medium and the housing must have inevitably so much length as the sum of those lengths. For that reason, it is very difficult to shorten the length of the housing.
In addition, in the conventional water hammer arrester, the internal pressure chamber is filled up with the air. The filled air comes to have a predetermined pressure which presses the piston. As the air shows, as well known, a big contraction or expansion rate, the internal pressure of air working on the piston is changed according to the change of the contraction or expansion rate of air by the rotation of seasons.
As the internal pressure of air corresponding to the fluid pressure working on the piston is changed by the change of the temperature, the conventional water hammer arrester having the internal pressure chamber filled up with air cannot completely function as a water hammer arrester.
Moreover, a connector such as a nipple connected to the pipe, as above described, is fixed to a lower part of the housing in the water hammer arrester. The connector is commonly formed as a screw part and screwed on the pipe line. Accordingly, the connector must keep an airtightness not to leak a fluid coming into the housing when the connector is connected to the pipe line. Conventionally, the two methods for fixing the connector to the housing are employed as follow.
The one method says that the lower part of the housing, as U.S. Pat. No. 4,819,698 shows, is provided with a screw part, which is connected to the connecting member such as a nipple. However, as the housing is rotated while the connecting member is connected to the pipe line, the method has a problem that a connection between the lower part of the housing and the connector is loosen. Accordingly, the problem is, a clearance between the lower part of the housing and the connector occurs and so a fluid like water or steam is leaked through the clearance.
The other method says that, as shown in U.S. Pat. No. 5,385,172 and No. 3,633,627, the nipple and the lower part of the housing are connected by the welding. This method has an advantage to reduce the leaking probability of the fluid in the connecting part. Nevertheless, the way of fixing the connector by the welding requires a welding work by hand, which needs many labors and has a low productivity and so the production cost increases.